Michael Jackson's mother has tearfully described finding out about her son's death and said she expressed concerns about his comeback concert schedule to promoters of the tour.

Katherine Jackson said she called the CEO of promoter AEG Live to express her view that her son could have done 50 shows, but not if they were spaced closely together.

"He couldn't do every other night like AEG wanted him to do at first," Katherine Jackson said.

She said she called AEG Live CEO Randy Phillips and her son's manager, Tohme Tohme, to express her concerns about the This Is It schedule. She did not describe any additional details about the calls.

Katherine Jackson is expected to be the final plaintiff's witness in her case against AEG Live, which has lasted 12 weeks. The defence case is scheduled to begin next week. She has been a courtroom fixture during the civil trial, sitting in the front row as witnesses described her son's creativity and interactions with AEG Live executives.

The Jackson family matriarch sued AEG Live in 2010 for negligence, claiming it failed to adequately investigate the doctor who was later convicted of involuntary manslaughter for giving the singer an overdose of anaesthetic in 2009. AEG denies it hired the doctor or bears any responsibility for the singer's death.

She said she also heard from her other children that Michael Jackson was abusing prescription medication, but she did not know what to believe. "He promised, he kept saying, 'I'm OK,'" she told the jury. "Sometimes the mothers are the last to know," she said.

Under questioning by AEG Live defence lawyer Marvin S Putnam, Katherine Jackson said it had been difficult to see and hear unflattering descriptions of her son. "It hurts to sit here and listen to all these things," she said. "To listen to how sick my son was and nobody was trying to help him."

She broke down as she described the day her son died. She said she was told by another of her son's managers, Frank Dileo. "I just started screaming," she said, crying and clutching a tissue in one of her hands.

Her lawyer, Brian Panish, asked her about her decision to sue AEG Live in September 2010. She said she did not discuss with her children or her grandchildren before filing the lawsuit.